1. Field of the Invention
The present invention relates to an apparatus and method of manufacturing synthetic boards from cellulosic or lignocellulosic furnish materials using an organic binder.
2. Description of the Prior Art
Many synthetic board products are manufactured using a thermosetting binder, heat and pressure to reconsolidate refined cellulosic and/or lignocellulosic furnish materials into a unitary finished board product. Examples of board manufacturing processes are shown in U.S. Pat. No. 2,757,115 to Heritage and U.S. Pat. No. 4,407,771 to Betzner et al. Basically, furnish material, such as wood, is reduced to fibers of the desired size by a refiner, mixed with a binder and other chemicals such as release and sizing agents, partially dewatered, formed into mats and compressed between heated platens in a hot press to form a board product of the desired thickness and density. In many current processes, the binder is applied to a rapidly moving stream of the fibers as it exits the refiner, in the so-called "blowline" of the process equipment. Alternatively, the binder may be added in the blender or elsewhere downstream of the refiner.
A wide variety of binder systems have been utilized in the production of synthetic boards, including various thermosetting organic binders, such as isocyanates, polyisocyanates, urea formaldehydes, phenolics, melamines and various mixtures thereof. Isocyanate and polyisocyanate binders have advantages over urea formaldehyde binders in that boards with greatly improved weather resistance can be produced. Processing time can typically be substantially reduced using isocyanate and polyisocyanate binders rather than standard phenolic binders. Although specially formulated phenolic binders can decrease the processing time, the cost of these specialty binders makes their use less attractive. Additionally, urea formaldehyde binders tend to produce formaldehydes, and phenolic binders tend to produce both formaldehydes and free phenols around the press area, which can cause significant health problems.
Heretofore, successful application of isocyanate binders in fiberboard manufacture has been limited due to many factors. First, there is often difficulty in achieving adequate distribution at low dosage rates. Second, many systems require the use of an expensive release agent-containing binder or must utilize a caul plate system which allows external release agent application. These problems usually result in increased production costs and/or inferior finished board product quality.
Many of the binder systems used today in board manufacture include an organic isocyanate binder which is specially mixed with a variety of diluent/extender agents to enhance binder distribution. These admixtures must also have a relatively long pot life to avoid premature curing, which can clog the binder delivery system. Unfortunately, even quite stable admixtures tend to deposit reaction products in process lines during use, and especially when use is interrupted. Both problems usually necessitate expensive machine downtime to unclog or replace components of the binder delivery system.
In systems utilizing isocyanate binders, the binder is typically formulated into an aqueous emulsion long before application to the furnish. Since the binder is highly reactive, the temperature during and after emulsification must be kept relatively low to avoid prereaction of the binder before it is applied to the furnish materials. Water-cooled addition devices, such as the nozzle described in U.S. Pat. No. 4,402,896 to Betezner et al have been used, but require a constant supply of cooling water and are still subject to clogging.
Another problem associated with specialty binders and their mixing equipment is that if the binder is not completely removed from the binder delivery system at the end of a production run, the binder will usually cure and clog the system. Therefore there is a need for a binder delivery system which assures that all of the binder is removed therefrom to avoid these problems.
Additionally, release agents are often added to the binder system to avoid sticking of the board to platens or caul plates during processing. However, these specially formulated binders are typically proprietary to a particular manufacturer and are prohibitively expensive for large-scale fiberboard manufacturing operations. Accordingly, there is a need for a process and apparatus which can utilize basic non-proprietary isocyanate and other binder compounds and release agents.
It is therefore an object of the present invention to provide a method of producing a synthetic board from cellulosic or lignocellulosic materials wherein standard, nonproprietary, inexpensive and readily available isocyanate, polyisocyanate and similar binders can be utilized, thus obviating the need for expensive specialty chemical formulations.
It is also an object of the present invention to provide an apparatus for producing a synthetic board wherein standard binders and release agents can be utilized.
It is a further object of the present invention to provide a method and an apparatus for forming a binder emulsion immediately upstream from the point of application to the wood fibers, thus allowing the use of isocyanates or polyisocyanates which do not form emulsions having extended stabilities or pot life.
It is also an object of the present invention to provide a method and apparatus for binder application wherein the emulsion is cooled by the diluent.
It is an object of the present invention to provide a method and apparatus for applying the binder which would avoid periodic plugging of the process equipment and the binder system.
It is also an object of the present invention to provide a method and apparatus for flushing the binder from the nozzle at the end of a production run so that the binder does not cure within the nozzle and clog the same.